Generation is a specific type of creation where entities are created without removing any other entity. In this manner, entities can be generated without removing any other entity or decreasing any resource. Most games with generation will place a limit on how often an entity can be generated in order to regulate the amount of entities generated.
In Gauntlet, monsters are generated from the generators. When a generator is removed, it can no longer generate monsters. If all the locations adjacent to the generator are occupied, the generator cannot generate monsters. The generator has a short delay between generations to prevent constant generation of monsters.
In Mega Man (2 through 8), the player can acquire abilities to summon his companion, Rush. Rush teleports to Mega Man's side to convey some benefit at the cost of weapon energy, and he departs after some time or usage constraint. The weapon energy cost is the "limit" placed on Rush's generation, though Rush can only be summoned once at a time (no duplicates, regardless of remaining energy).